Fix a Leaking Pipe Under the Sink
A drip under the sink is usually a loose slip-joint nut or a worn washer — not a broken pipe. This guide walks you through finding the exact drip, tightening first, and replacing the trap washers the right way round.
What is actually broken
Nine times out of ten it's not the pipe itself — it's a slip-joint nut that has loosened or a rubber washer inside it that has gone hard and cracked. The P-trap (the U-shaped section) is designed to come apart by hand precisely so you can fix this without cutting anything.
Safety first
- Put a bucket under the trap before loosening anything — the trap holds a cup or two of dirty water by design.
- If the pipe is copper or galvanized and corroded green/white, don't force it — see the stop note below.
The fix, step by step
1 Dry everything and find the exact drip
Empty the cabinet, put a bucket under the trap, and dry every pipe and joint with a paper towel. Run the tap for 30 seconds, then watch: the first wet spot is your leak. A dry paper towel touched to each joint makes slow seeps easy to spot.
Tip: Most leaks are at the slip-joint nuts — the big plastic or metal rings where pipe sections meet.
2 Hand-tighten the slip-joint nuts first
Try this before taking anything apart: grip each slip-joint nut on the leaking joint and turn it clockwise by hand, snug and firm. Run the water again. A surprising number of these leaks stop right here — the nuts loosen slowly from vibration and use.
Tip: Plastic nuts should only ever be hand-tight. Tools crack them.
3 Take the trap apart
If it still drips, unscrew the two slip-joint nuts holding the U-bend (the P-trap) and drop it into the bucket. Note the order: nut, then a thin beveled rubber or nylon washer on each pipe end. Take a photo before you pull it fully apart so reassembly is obvious.
Tip: The trap holds standing water on purpose — it blocks sewer gas. Expect the smell; it's normal.
4 Replace the washers
Take the old washers to match the size (1¼" for bathroom sinks, 1½" for kitchen). Fit the new beveled washer onto each pipe end with the bevel (tapered side) facing INTO the joint it seals against. If the pipe ends are scratched or the trap itself is cracked, replace the whole trap — a full kit is under $10.
Tip: Washer orientation is the #1 reason a 'fixed' trap still leaks. Bevel toward the joint, always.
5 Reassemble hand-tight
Slide everything back together, start all the nuts by hand so nothing cross-threads, then snug them firmly by hand. The sections should line up without being forced — if you have to pull a pipe sideways to meet, loosen, realign, and retry.
Tip: No pipe dope or Teflon tape on slip joints — the washer does the sealing.
6 Test with a full sink
Run the tap for a full minute, then fill the sink and pull the plug — the rush of a draining sink is the real pressure test. Run a dry paper towel around every joint. No dampness after two drain cycles means you're done.
Tip: Leave the bucket under there overnight as cheap insurance on your first repair.
Stop and call a pro if…
Stop and call a plumber if you find cracked or corroded metal pipe, a leak coming from inside the wall, or water damage/mold on the cabinet floor — those are bigger jobs than a washer swap.
Your work, your responsibility
If you do this repair yourself: you attempt it entirely at your own risk. This guide is general information, not professional advice, and it can be wrong or incomplete. ClickTheFix is not responsible for injury to you or anyone else, or for damage to your property, that results from following — or misfollowing — this guide. Follow the safety warnings, use proper protective gear, follow the manufacturer's instructions and your local codes, and stop if any step is beyond your skill or comfort.
If a contractor does the work: any contractor you hire is an independent professional working under an agreement between you and them alone. ClickTheFix does not provide repair services, does not supervise or control their work, and does not guarantee or warranty it. ClickTheFix is not liable for a contractor's errors, omissions, poor workmanship, property damage, or injuries.